Filter cartridge and process for producing the same

ABSTRACT

An object of the present invention is to provide a filter cartridge having an high filtering accuracy, a long filter life and a good liquid-passing property, in which an initial trapped particle diameter little changes, a pressure loss is small and neither bubbling nor falling of the filter material is observed. Such a filter cartridge is obtained by a production process, which comprises winding a non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein a non-woven fabric strip satisfies the following equation (A):  
     log 10   Y&lt;   3.75−0.6 (log 10   X )  (A)  
     wherein X (cm 3 /cm 2 /sec) is an airflow amount of the non-woven fabric strip, and Y (g/m 2 ) is a basis weight thereof; or a production process, which comprises winding in a twill form, wherein a number (W) of winding a non-woven fabric strip around a perforated cylinder from one end to the other end is one to 10 per a length of 250 mm in the perforated cylinder.

FIELD OF THE INVENTION

[0001] The present invention relates to a filter cartridge and a processfor producing the same, specifically to a cylindrical filter cartridgewhich is prepared by winding a non-woven fabric strip comprisingthermoplastic fibers on a perforated cylinder in a twill form and whichis excellent in a liquid-passing property, a filter life and stabilityof a filtering accuracy, and a process for producing the same.

BACKGROUND OF THE INVENTION

[0002] Various filters for clarifying a fluid are presently developedand produced. Among them, cartridge-type filters (hereinafter calledfilter cartridges) are widely used in the industrial field, for example,for removing suspended particles in industrial liquid materials,removing cakes flowing out of a cake filtering apparatus and clarifyingindustrial water.

[0003] Several kinds of structures of a filter cartridge have so farbeen proposed. The most typical one is a bobbin winder-type filtercartridge, which is a cylindrical filter cartridge prepared by winding aspun yarn as a filter material on a perforated cylindrical core in atwill form and then fluffing the spun yarn. This type has long been useddue to inexpensiveness and easiness in production. Another type ofstructure includes a non-woven fabric-laminated type filter cartridge.This is a cylindrical filter cartridge prepared by winding several kindsof non-woven fabrics such as a carding non-woven fabric stepwise andconcentrically on a perforated cylindrical core. A recent advancedtechnique in a non-woven fabric production has allowed some of them tobe put to practical use.

[0004] However, the above-mentioned filter cartridges have severaldefects. For example, in the bobbin winder-type filter cartridge fortrapping foreign matters by means of fluffs of fluffed spun yarns andalso in gaps of the spun yarns, it is difficult to control the size andform of the fluffs and gaps. This limits size and amount of the foreignmatters that can be trapped. Further, constitutional fibers of a spunyarn, which is made from short fibers, fall away when fluid flows ontothe filter cartridge.

[0005] Furthermore, in producing a spun yarn, a trace amount of asurfactant is often applied onto a surface of material short fibers toprevent the short fibers from sticking to a spinning machine byelectrostatic charge or the like. Filtering a liquid by means of afilter cartridge using surfactant-coated spun yarns may bring adverseeffects on the cleanness of liquid, such as foaming of the liquid, andincrease in TOC (total organic carbon), COD (chemical oxygen demand) andthe electric conductivity. In addition, a spun yarn is produced byspinning short fibers as already mentioned, for which at least two stepsof forming and spinning short fibers are required. Thus, use of the spunyarn will sometimes increase a price of the product.

[0006] A performance of a non-woven fabric-laminated type filtercartridge depends on the non-woven fabric used. A non-woven fabric isproduced mostly by a method in which short fibers are confounded bymeans of a carding machine or an air laid machine and then subjectingthem, if necessary, to heat treatment by means of a hot-air heater or aheating roll, or a method in which a non-woven fabric is directlyprepared, such as a melt blowing method and a spun bonding method.However, any machines used for producing non-woven fabrics, such as acarding machine, an air laid machine, a hot-air heater, a heating roll,a melt blowing machine and a spun bonding machine, may cause, forexample, uneven basis weights of a non-woven fabric in a lateraldirection of a machine. Accordingly, a filter cartridge of poor qualitywill be produced. Also, use of a more advanced manufacturing techniqueto avoid such unevenness sometimes raises the production cost. Moreover,production of one kind of non-woven fabric-laminated type filtercartridges needs two to six kinds of non-woven fabrics, and differentnon-woven fabrics are needed depending on the kind of a filtercartridge. Thus, the production cost will increase in some cases.

[0007] Several methods have been proposed in order to solve suchproblems of conventional filter cartridges. For example, JapaneseUtility Model Publication No. 6-7767 proposes a filter cartridge inwhich a filter material obtained by squashing a tape-shaped paper havingporosity while twisting, thereby squeezing it to control a diameterthereof to about 3 mm is wound around a porous internal cylinder in aclose twill. This method is advantageous in that a winding pitch can begradually increased from the porous internal cylinder toward theoutside. However, the filter material needs to be squashed and squeezed,so that foreign matters are trapped primarily between the windingpitches of the filter material. Accordingly, it is less expected to trapforeign matters by the filter material itself as is the case of aconventional bobbin winder type filter using spun yarns which trapsforeign matters by means of fluffs. This blocks the surface of thefilter to shorten the filter life or brings about the poorliquid-passing property in a certain case.

[0008] JP-A 1-115423 proposes a filter in which strings obtained byslitting a cellulose spun bonded non-woven fabric into strips andpassing them through narrow holes to twist them are wound around abobbin having a lot of drilled pores. It is considered that this methodshall make it possible to prepare a filter having a higher mechanicalstrength and being free of dissolution in water and elution of a binder,as compared with a conventional roll tissue filter prepared by windingtissue paper in a roll form, which is produced from a-cellulose preparedby refining a coniferous pulp.

[0009] However, the cellulose spun bonded non-woven fabric used for thisfilter has a papery form and thus a too high rigidity, so that it isless expected to trap foreign matters by the filter material itself asis the case of a conventional bobbin winder type filter using spun yarnswhich traps foreign matters by means of fluffs. Further, the cellulosespun bonded non-woven fabric is liable to swell in a liquid due to itspapery form. Swelling may bring about various problems such as adecrease in a filter strength, a change in a filtering accuracy, adeterioration in a liquid-passing property, a reduction in a filter lifeand the like. Adhesion at fiber intersections of the cellulose spunbonded non-woven fabric are mostly conducted by a certain chemicaltreatment. Such adhesion is often unsatisfactory, causing a change in afiltering accuracy or falling of fiber chips, so that a stable filteringperformance is difficult to achieve.

[0010] Further, JP-A 4-45810 proposes a filter prepared by winding aslit non-woven fabric comprising composite fibers in which 10% by weightor more of structural fibers is divided ones of 0.5 denier or less on aporous core cylinder to provide the fiber density of 0.18 to 0.30. Thismethod is advantageously used to trap fine particles contained in aliquid by means of fibers having a high fineness. However, in order todivide the composite fibers, a stress needs to be applied using, forexample, high-pressure water, and it is difficult to evenly divide thefibers all over the non-woven fabric by means of high-pressure waterprocessing. If not evenly divided, there occurs a difference in atrapped particle diameter between a well-divided portion and aninsufficiently divided portion of the non-woven fabric, and this maylower the filtering accuracy. Further, the stress applied for dividingsometimes lowers a strength of the non-woven fabric, and this may causereduction of the resulting filter strength and frequent deformation ofthe filter during use; or possible change of the void ratio of thefilter may reduce the liquid-passing property.

[0011] Further, the reduced strength of the non-woven fabric makes itdifficult to control a tension in winding around a porous core cylinder,and hence the difficulty in exact control of the void rate may arise.Further, a spinning technique required for producing easily divisiblefibers and an increased operation cost in producing thereof lead to anincreased production cost of the filter. Such a filter would be usablein a certain field such as the pharmaceutical industry and theelectronic industry which require a high filtering performance, if theabove mentioned problems of the filtering performance are solved.However, such a filter is considered to be difficult to use in cases inwhich inexpensive filters are requested such as the filtering ofswimming pool water and a plating liquid for the plating industry.

[0012] An object of the present invention is to provide a cylindricalfilter cartridge which is excellent in a liquid-passing property, afilter life and stability of a filtering accuracy.

[0013] An object of the present invention is to solve the problemsdescribed above. It has been found, as a result of investigations, thata cylindrical filter cartridge which is excellent in a liquid-passingproperty, a filter life and a stability of a filtering accuracy can beobtained by winding a long fiber non-woven fabric comprisingthermoplastic fibers on a perforated cylinder in a twill form.

SUMMARY OF THE INVENTION

[0014] The present inventors have conducted intensive researches and, asa result, found that the problems described above can be solved by acylindrical filter cartridge, which is prepared by winding a non-wovenfabric strip on a perforated cylinder in a twill form, in which thestrip is a long fiber non-woven fabric and/or a melt blown non-wovenfabric comprising thermoplastic fibers and an airflow amount (airpermeability) is specially related to a basis weight; or by specifying anumber of winding in producing the filter cartridge. This finding hasled to the present invention.

[0015] The present invention is composed of:

[0016] (1) A filter cartridge which is prepared by winding a non-wovenfabric strip comprising a thermoplastic fiber around a perforatedcylinder in a twill form, wherein the non-woven fabric strip satisfiesthe following equation (A):

log₁₀ Y<3.75−0.6(log₁₀ X)  (A)

[0017] wherein X (cm³/cm²/sec) is an airflow amount of the non-wovenfabric strip measured in accordance with JIS L 1096-A (1990), and Y(g/m²) is a basis weight thereof.

[0018] (2) A filter cartridge which is prepared by winding a long fibernon-woven fabric strip comprising a thermoplastic fiber around aperforated cylinder in a twill form, wherein the non-woven fabric stripsatisfies the following equation (B):

log₁₀ Y<3.75−0.75(log₁₀ X)  (B)

[0019] wherein X (cm³/cm²/sec) is an airflow amount of the non-wovenfabric strip measured in accordance with JIS L 1096-A (1990), and Y(g/m²) is a basis weight thereof.

[0020] (3) A filter cartridge which is prepared by winding a non-wovenfabric strip comprising a thermoplastic fiber around a perforatedcylinder in a twill form, wherein in winding in a twill form, a number(W) of winding the non-woven fabric strip from one end to the other endin a longitudinal direction of the perforated cylinder is one to 10 pera length of 250 mm in the perforated cylinder.

[0021] (4) The filter cartridge as described in the item (3), whereinwhen a 2-fold value (2W) of the winding number (W) is represented by afraction having a denominator of two figures or less which is anon-reducible approximate value, the denominator is 4 to 40.

[0022] (5) The filter cartridge as described in any one of the items (1)to (3), wherein at least a part of fiber intersections of the non-wovenfabric strip is thermally bonded.

[0023] (6) The filter cartridge as described in any one of the items (1)to (3), wherein the non-woven fabric strip has a width of 0.5 to 40 cm.

[0024] (7) The filter cartridge as described in any one of the items (1)to (3), wherein a product of a width (cm) and a basis weight (g/m²) ofthe non-woven fabric strip is 10 to 200.

[0025] (8) The filter cartridge as described in any one of the items (1)to (3), wherein the non-woven fabric strip has a thickness of 0.02 to1.20 mm.

[0026] (9) The filter cartridge as described in any one of the items (1)to (3), wherein the non-woven fabric strip is thermal compression bondedby means of a heat embossing roll having an embossing area rate of 5 to25%.

[0027] (10) The filter cartridge as described in any one of the items(1) to (3), wherein the filter material of the filter cartridge has avoid rate of 65 to 85%.

[0028] (11) The filter cartridge as described in the item (1) or (3),wherein the non-woven fabric strip is of a long fiber non-woven fabric.

[0029] (12) The filter cartridge as described in the item (11), whereinthe long fiber non-woven fabric is produced by a spun bonding method.

[0030] (13) The filter cartridge as described in the item (1) or (3),wherein the non-woven fabric strip is of a melt blown non-woven fabric.

[0031] (14) The filter cartridge as described in any one of the items(1) to (3), wherein the thermoplastic fiber is a composite fibercomprising a low melting resin and a high melting resin, a difference ofthe melting points between these resins being 10° C. or more.

[0032] (15) The filter cartridge as described in any one of the items(1) to (3), wherein the thermoplastic fiber is a fiber formed from atleast one thermoplastic resin selected from the group consisting of apolyester resin, a polyamide resin, a polyethylene resin and apolypropylene resin.

[0033] (16) A process for producing a filter cartridge, which compriseswinding a non-woven fabric strip comprising a thermoplastic fiber arounda perforated cylinder in a twill form, wherein the non-woven fabricstrip satisfies the following equation (A):

log ₁₀ Y<3.75−0.6(log ₁₀ X)  (A)

[0034] wherein X (cm³/cm²/sec) is an airflow amount of the non-wovenfabric strip measured in accordance with JIS L 1096-A (1990), and Y(g/m²) is a basis weight thereof.

[0035] (17) A process for producing a filter cartridge, which compriseswinding a non-woven fabric strip comprising a thermoplastic fiber arounda perforated cylinder in a twill form, wherein in winding in a twillform, a number (W) of winding the non-woven fabric strip from one end tothe other end in a longitudinal direction of the perforated cylinder isone to 10 per a length of 250 mm in the perforated cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a conceptual diagram of a spun bonded non-woven fabric.

[0037]FIG. 2 is a conceptual diagram of a short fiber non-woven fabric.

[0038]FIG. 3 represents the equation (A) showing a relation of a basisweight to an airflow amount of the non-woven fabric.

[0039]FIG. 4 is an illustration of winding a non-woven fabric strip asit is, without processing.

[0040]FIG. 5 is an illustration of winding a non-woven fabric strip withtwisting.

[0041]FIG. 6 is an illustration of winding a non-woven fabric strip withtraversing.

[0042]FIG. 7 is an illustration of trapping foreign matters by means ofan embossing pattern of a non-woven fabric.

[0043]FIG. 8 is a perspective of the filter cartridge according to thepresent invention.

[0044] Explanation of Codes

[0045]1: Long fiber constituting spun bonded non-woven fabric

[0046]2: Foreign matters

[0047]3: Bobbin

[0048]4: Perforated cylinder

[0049]5: Traverse guide

[0050]6: Non-woven fabric strip or converged matter thereof

[0051]7: Filter cartridge

[0052]8: Part where strong thermal compression bonding by an embossingpattern is applied.

[0053]9: Part where only weak thermal compression bonding by deviatingfrom an embossing pattern is applied

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0054] The embodiment of the present invention shall be explained belowin detail.

[0055] The filter cartridge of the present invention is prepared bywinding a non-woven fabric strip comprising a thermoplastic fiber on aperforated cylinder in a twill form.

[0056] In the present invention, the non-woven fabric strip means anon-woven fabric having a narrow width, which is prepared by slitting(cutting) a wide non-woven fabric or produced directly in a narrowwidth. It is preferable that a wide non-woven fabric is slit in order toobtain the stable quality at low cost. An optimum width and basis weightof a non-woven fabric to be used shall be described later.

[0057] In the present invention, the thermoplastic fiber means a fiberproduced from a thermoplastic resin. All thermoplastic resins capable ofbeing melt-spun can be used for the thermoplastic resin used in thepresent invention.

[0058] Examples include polyethylene resins such as low densitypolyethylene, high density polyethylene and linear low densitypolyethylene; polypropylene resins such as polypropylene andcopolymerized polypropylene (for example, binary or multi-componentcopolymers comprising propylene as a primary component with ethylene,butene-1, 4-methylpentene-1 and the like); other polyolefin resins thanthe above polyethylene and polypropylene resins; polyester resins suchas polyethylene terephthalate, polybutylene terephthalate and lowmelting polyesters copolymerized with addition of isophthalic acidbesides terephthalic acid as an acid component; polyamide resins such asnylon 6 and nylon 66; and thermoplastic resins such as polystyrene,polyurethane elastomers, polyester elastomers andpolytetrafluoroethylene.

[0059] Functional resins can also be used so as to provide a filtercartridge with a biodegradability derived from biodegradable resins suchas a lactic acid base polyester. Further, polyolefin resins andpolystyrene resins which can be polymerized using metallocene catalystsare preferably used for a filter cartridge, taking advantage of thecharacteristics of metallocene resins such as improvements in a strengthof a non-woven fabric and a chemical resistance, and a reduction in aproduction energy.

[0060] Also, those resins may be blended for use in order to control aheat adhesion property and a rigidity of a non-woven fabric. When afilter cartridge is used for filtering an aqueous solution of roomtemperature, polyolefin resins such as polypropylene and polyethyleneare preferably used from the viewpoints of a chemical resistance and acost. When used for a solution of a relatively high temperature,polyester resins and polyamide resins are preferred.

[0061] These thermoplastic resins can be blended, if necessary, withpublicly known additives.

[0062] The non-woven fabric strip used in the present invention ispreferably a long fiber non-woven fabric or a melt blown non-wovenfabric, and the resulting filter cartridge reduces a risk that fibersfall off and are mixed in a filtrate when used for filtering.

[0063] The long fiber non-woven fabric or melt blown non-woven fabricdescribed above can be used separately as a non-woven fabric strip or inthe form of a laminated non-woven fabric of the both.

[0064] In the filter cartridge of the present invention, the melt blownnon-woven fabric as the non-woven fabric strip has a higher finenessthan that of the long fiber non-woven fabric, and the texture thereofcan easily be homogenized. Accordingly, the resulting filter cartridgecan be improved in a filtering accuracy.

[0065] An average fiber diameter of the above melt blown non-wovenfabric varies depending on uses of the filter cartridge and kinds of theresin, and is 0.5 to 1000 μm, preferably 1 to 50 μm. If the averagefiber diameter is less than 0.5 μm, it is difficult to produce thenon-woven fabric, which may result in a high-cost filter cartridge. Onthe other hand, the average fiber diameter exceeding 1000 μm expands adistribution of the fiber diameter and deteriorates a texture of theresulting non-woven fabric. Further, the average fiber diameterexceeding 50 μm may allow the adjacent fibers to bond each other byremaining heat, but it makes no difference especially as long as it doesnot prevent the effects of the present invention.

[0066] The non-woven fabric strip used in the present invention ispreferably a long fiber non-woven fabric, a melt blown non-woven fabricor a laminated non-woven fabric thereof, in which at least a part offiber intersections thereof is thermally bonded. Among them, preferredis the long fiber non-woven fabric in which at least a part of fiberintersections thereof is thermally bonded.

[0067] In particular, a non-woven fabric obtained by a spun bondingmethod is preferred as the long fiber non-woven fabric described above.The spun bonding method is a non-woven fabric production technique inwhich a thermoplastic fiber discharged from a nozzle is sucked and drawnby an air gun, spread on a conveyor and then thermally bonded. The longfiber non-woven fabric comprising thermoplastic fibers produced by thespun bonding method has a fiber direction aligned along a machinedirection as shown in FIG. 1, so that a hole constituted by fibers 1becomes long and narrow, and a maximum size of the passing particle 2 israther small. In contrast with this, a non-woven fabric comprising shortfibers obtained by a carding method and the like has a fiber directionnot fixed as shown in FIG. 2, so that a hole constituted by fibers 1 hasa shape close to a circle or a square, and a maximum size of the passingparticle 2 is larger than that of a long fiber non-woven fabric producedby the spun bonding method, even the two has the same fiber diameter andvoid rate.

[0068] In the present invention, other fibers than the thermoplasticfiber, for example, cotton, glass fibers and metallic fibers can be usedin combination as structural fibers of the non-woven fabric strip aslong as they do not impair a filter life, a liquid-passing property andthe functions such as preventing matters from falling off the filtercartridge which are characteristics of the present filter cartridge.

[0069] In the non-woven fabric strip used for producing the filtercartridge which is the first embodiment of the present invention, anairflow amount X (cm³/cm²/sec) and a basis weight Y (g/m²) which aremeasured by a JIS L 1096-A method satisfy the following equation (A) bybonding the fiber intersections thereof.

log ₁₀ Y<3.75×0.6(log ₁₀ X)  (A)

[0070] The filter cartridge of the present invention which is preparedby winding the non-woven fabric strip around a perforated cylinder in atwill form exhibits an excellent filtering accuracy.

[0071] A relation of the equation (A) is shown in FIG. 3. The equation(A) represents a shaded area in FIG. 3 and exhibits a basis weight rangecorresponding to the respective airflow amounts of the non-woven fabricstrip. When the airflow amount and the basis weight do not have arelation represented by the shaded area, it means that the basis weightis too large, and a rigidity of the non-woven fabric strip becomes toohigh, so that it is difficult to minutely wind the non-woven fabricstrip around the perforated cylinder, and the resulting filter cartridgemay have a reduced filtering accuracy.

[0072] If the production process of the present invention is a spunbonding process in which a non-woven fabric is prepared directly from aformed fiber, the resulting filter cartridge reduces a risk that thefibers fall off and are mixed in the filtrate when used for filtering.Further, it is relatively low in cost, and therefore, it is preferable.

[0073] In the second embodiment of the present invention, the non-wovenfabric strip is a long fiber non-woven fabric, and the airflow amount X(cm³/cm²/sec) and the basis weight Y (g/m²) satisfy the followingequation (B). In such a case, the filter cartridge is excellent in anon-woven fabric strength and a property of preventing the fibers fromfalling off the filter cartridge, and therefore it exhibits aparticularly excellent filtering accuracy.

log ₁₀ Y<3.75−0.75(log ₁₀ X)  (B)

[0074] Next, a method for winding the non-woven fabric strip around aperforated cylinder shall be explained. One example of the processes isshown in FIG. 4. A winder conventionally used for a bobbin winder typefilter cartridge can be used for the winding machine. A perforatedcylinder 4 having a diameter of about 10 to 40 mm and a length of 100 to1000 mm is installed to a bobbin 3 of this winder. A non-woven fabricstrip 6 passes through a yarn passage and a hole of a traverse guide 5of the winder to be converged and wound around the perforated cylinderone to two times. The perforated cylinder may be thermally bonded to anend part of the non-woven fabric strip in order to accurately wind thestrip. The yarn passage of the winder is waved in each longitudinaldirection in a twill form by means of the traverse guide 5 disposedparallel to the bobbin, so that the non-woven fabric strip is woundaround the perforated cylinder in a twill form by rotation of thebobbin, whereby a filter cartridge 7 is produced. A diameter of the holedisposed in the traverse guide 5 varies depending on a basis weight anda width of the non-woven fabric strip used and falls preferably in arange of 3 to 10 mm. If this diameter is less than 3 mm, a frictionbetween the non-woven fabric strip and the hole is increased, so thatthe winding tension becomes too high. On the other hand, the valuelarger than 10 mm may not render the converging size of the non-wovenfabric stabilized. Various traverse guides having a narrow hole can beused for the traverse guide 5. For example, those in an almost circularform, an almost elliptical form and an almost flat form can be used.Further, those having an aperture part at one end of a narrow hole canbe used as well.

[0075] The perforated cylinder functions as a core of a filtercartridge, and the material and the form thereof shall not specificallybe restricted as long as it has a strength which is endurable toexternal pressure applied in filtering and the pressure loss is notmarkedly high. It may be, for example, an injection-molded articleobtained by processing polyethylene or polypropylene into a net typecylinder as is the case with a core used for a conventional filtercartridge or ones obtained by processing ceramics and stainless steel inthe same manner. Alternatively, other filter cartridges such as a filtercartridge subjected to pleat-folding processing and a filter cartridgeof a non-woven fabric-winding type can be used as a perforated cylinder.

[0076] The winding conditions in this case can be set up according tothose in producing a conventional bobbin winder type filter cartridge.Initial speed of the bobbin may be set to, for example, 1000 to 2000rpm, and the feeding speed may be controlled to apply a tension inwinding the non-woven fabric. The void rate of the filter cartridge canbe changed by the tension in this case.

[0077] On the other hand, this non-woven fabric strip can be twisted andthen wound. One embodiment of the production process is shown in FIG. 5.Also in this case, a winder conventionally used for a bobbin winder typefilter cartridge can be used for the winding machine. The non-wovenfabric becomes apparently thick by twisting, and therefore a traverseguide 5 has preferably a larger hole diameter than that in the case ofFIG. 4. By twisting a non-woven fabric, an apparent void rate of thenon-woven fabric can be changed depending on a twisting number per unitlength or a twisting strength, so that the filtering accuracy can becontrolled. The twisting number in this case falls preferably in a rangeof 50 to 1000 times per meter of the non-woven fabric strip. If thisvalue is smaller than 50 times, the twisting effect is scarcelyobtained. On the other hand, the value larger than 1000 times willprovide the filter cartridge produced with a inferior liquid-passingproperty. Accordingly, both are not preferred.

[0078] It is more preferred to converge the non-woven fabric strip byany method and then wind it around a perforated cylinder. Such a methodinclude one in which the non-woven fabric strip may be passed merelythrough a small hole to be converged or one in which the cross-sectionalform of the non-woven fabric strip may be pre-molded by means of apleat-forming guide and then passed through a small hole to be processedinto a pleated matter. Use of the latter method makes it possible tocontrol a ratio of a traversing speed of the traverse guide to arotating speed of the bobbin to change the winding pattern, so thatfilter cartridges having various performances can be produced from thesame kind of the non-woven fabric strip.

[0079] One embodiment of a production process in which the non-wovenfabric is passed merely through a small hole for converging the strip isshown in FIG. 6. Also in this case, a winder conventionally used for abobbin winder type filter cartridge can be used for the winding machine.In FIG. 6, the hole of a traverse guide 5 turned into a small hole,thereby converging the non-woven fabric strip, but a guide of a smallhole may be provided at a yarn passage in front of the traverse guide 5.The diameter of the small hole varies depending on the basis weight andthe width of the non-woven fabric used and falls preferably in the rangeof 3 to 10 mm. If this diameter is smaller than 3 mm, a friction betweenthe non-woven fabric and the small hole is increased, so that thewinding tension becomes too high. On the other hand, the value largerthan 10 mm may not render the converging size of the non-woven fabricstabilized.

[0080] Further, when producing the above non-woven fabricstrip-converged matter, granular activated carbon or ion exchange resinsmay be present as long as they do not damage the effects of the presentinvention. In this case, in order to fix granular activated carbon orion exchange resins, they may be bonded by means of a suitable bindereither prior to or after converging the non-woven fabric strip orprocessing it into a pleated matter, or they may be first added and thenthermally bonded to the structural fibers of the non-woven fabric byheating.

[0081] The yarn passage of the winder is waved in twill form by means ofa traverse cam disposed parallel to the bobbin, so that the non-wovenfabric strip is wound around the perforated cylinder while waving in atwill form. The winding conditions in this case can be set up accordingto those in producing a conventional bobbin winder type filtercartridge. Initial speed of the bobbin may be set to, for example, 1000to 2000 rpm, and the feeding speed may be controlled to apply a tensionin winding the non-woven fabric. The void rate of the filter cartridgecan be changed by the tension in this case.

[0082] Further, the tension in winding is controlled to make the voidrate of an internal layer small, and the void rate of an intermediatelayer to an external layer gradually large as the non-woven fabric iswound around. In particular, when the non-woven fabric strip is firstformed into the pleated matter and then is wound around the perforatedcylinder, there can be provided a filter cartridge having an idealfiltering structure owing to a difference in rough and dense structuresformed in the external layer, the intermediate layer and the internallayer in combination with a deep layer-filtering structure formed by thepleats of the pleated matter.

[0083] The filtering accuracy can be changed by controlling a ratio ofthe traversing speed of the traverse cam to the rotating speed of thebobbin, thereby changing a number (hereinafter referred to as a windingnumber and represented by W) of winding the non-woven fabric striparound the perforated cylinder from one end to the other end in alongitudinal direction when winding the non-woven fabric strip in atwill form. That is, the winding number means a rotation number of thebobbin 3 while the traverse guide 5 moves from one end to the other endof the perforated cylinder 4 in a longitudinal direction. Accordingly, avalue of W is not necessarily a natural number. The winding numbershould be very accurate, and therefore, a moving distance of thetraverse guide has to be geared to a rotation number of the bobbin sothat this value should not get out of order.

[0084] In the filter cartridge of the present invention, a windingnumber W is 1 to 10, preferably 2 to 8 and more preferably 3 to 5 per250 mm of the perforated cylinder used for the filter cartridge. If thisvalue is less than one, an angle of traversing becomes too large, andtherefore the non-woven fabric strip is liable to get out of theperforated cylinder. On the other hand, if this value exceeds 10, anangle of traversing becomes too small, and the non-woven fabric strip isliable to get out of the perforated cylinder also in this case. Further,if the value deviates from the range of 1 to 10, an initial trappedparticle diameter becomes extremely large, resulting in an inadequatefilter cartridge.

[0085] A relation of the winding number to the filtering accuracy iswell known in the case of a wound filter in which a spun yarn is used asa filtering material. In a conventional wound filter in which a spunyarn is used, a winding yarn (that is, a spun yarn) generally has acircular cross-sectional form, and a yarn diameter thereof is about 3 mmat the largest. Thus, the winding number and the pitch of the yarn inwinding in a twill form can be represented by the following equations(1) and (2):

2×W=2×W ₀±1/N  (1)

N=T/W ₀ /P  (2)

[0086] wherein W is a winding number; W₀ is a natural number approximateto the winding number W; N is an ordered number; T is a traverse width;and P is a pitch of the yarn. Among the above variables, W₀ and N arenatural numbers, and W, P and T are arbitrary positive numbers. Ingeneral, as the pitch of the yarn becomes smaller, the wind filterhaving a finer accuracy is prepared. This equation can be applied to ayarn other than a spun yarn, for example, a split yarn.

[0087] On the other hand, in the filter cartridge of the presentinvention, the non-woven fabric strip is used as a filter material inplace of a spun yarn, and therefore the equations (1) and (2) cannot beapplied as they are. The non-woven fabric is converged in winding asdescribed above, so that a thickness of the yarn becomes far large ascompared with that of a conventional spun yarn. Accordingly, even if theconditions of the equations (1) and (2) are satisfied, the yarnsthemselves are superposed and a filter cartridge having the intendedaccuracy is not obtained.

[0088] As the third embodiment of the present invention, we have foundthat a filter cartridge, which is prepared by winding a non-woven fabricstrip around a perforated cylinder in a twill form, exhibits anexcellent filtering performance when a denominator M_(n) is a specificvalue the winding number approximated by the following equation (3):

2×W≈X/M _(n)  (3)

[0089] wherein X/M_(n) represent a non-reducible fraction, X and M_(n)are each independently natural numbers, and n represents a maximumfigure of the number; for example, M₂ is an integer of 1 to 99.

[0090] In the present invention, when a 2-fold value (2W) of the windingnumber (W) is represented by an approximate fraction having anon-reducible denominator of two figures or less, M₂ in the equation(3), i.e., a value of the denominator is 4 to 40, preferably 5 to 20. Asthe value of M₂ becomes larger, the filter cartridge having a finertexture is prepared. If this value is less than 4, a texture of theresulting filter cartridge is roughened too much, and it is likely thata filter cartridge end face is not smooth. On the other hand, if thevalue of M₂ exceeds 40, a texture of the filter cartridge becomes toofine, and it is likely that the liquid-passing property is reduced andthe filter life is shortened.

[0091] In this case, it is important that the value of 2W is approximateto a fraction having a denominator of a natural number of two figures orless. For example, when the winding number is 1.893, 2×W is 3.786. Whenthis 3.786 is approximated to a fraction having a denominator of onefigure, it is 3 and ⅘ (this means a mixed fraction consisting of 3 andfour fifths, and the same shall apply unless otherwise described).Accordingly, when the winding number is 1.893, M₁ is 5 which is thedenominator of 3 and ⅘. Similarly, when 2W is approximated to a fractionhaving a denominator of two figures or less, a value thereof is 3 and{fraction (11/14)}, and therefore M₂ is 14 which is a denominator of 3and {fraction (11/14)}. Similarly, when 2W is approximated to a fractionhaving a denominator of three figures or less, it is 3 and {fraction(393/500)}, and therefore M₃ is 500. Accordingly, in this case, a valueof M₂ in the equation (3) is 14 which is the denominator whenapproximated to a fraction having a denominator of two figures. When 2Wis approximated to a fraction having a denominator of two figures orless, 3 and {fraction (22/28)} and 3 and {fraction (33/42)} are also themost approximate values, but these number are reduced to 3 and {fraction(11/14)}, so that a value of M₂ is 14 in this case.

[0092] The value of M₂ described above is varied in a range of 4 to 40,whereby filter cartridges having various accuracies can be prepared evenif the same non-woven fabric strip is used. Further, it can also becombined with a method of varying a width, a basis weight or a fiberdiameter of the non-woven fabric strip.

[0093] A deep layer-filtering structure of the filter cartridge canfurther be optimized by winding the non-woven fabric with M₂ set to aspecific value until the major diameter becomes a certain degree, and byfurther winding the non-woven fabric with the value of M₂ changed.

[0094] In the filter cartridge of the present invention, the non-wovenfabric strip is wound around the perforated cylinder 2 to form a filtercartridge having a major diameter 1.5 to 3 times as large as that of theperforated cylinder. Even when wound in the same winding number, a spacebetween the non-woven fabric strips is varied depending on a majordiameter of the perforated cylinder 4. A major diameter of theperforated cylinder 4 is usually decided according to use conditions,and the filtering performance is not controlled by a major diameter ofthe perforated cylinder 4. If the winding number is the same, as themajor diameter of the filter cartridge becomes larger, the particlediameter of the initial particles trapped on the filter cartridgebecomes smaller.

[0095] A fiber diameter of the long fiber used for the long fibernon-woven fabric described above varies depending on uses of the filtercartridge and kinds of the resin, and it is preferably in a range of 5to 680 μm. If the fiber diameter exceeds 680 μm, it makes no differencebetween continuous yarns merely bound into a bundle and the long fibernon-woven fabric. On the other hand, even if the fiber diameter is lessthan 5 μm, the resulting long fiber non-woven fabric can be used for afilter cartridge. However, when the long fiber non-woven fabric is anon-woven fabric prepared by a spun bonding method as described above(hereinafter referred to as a spun bonded non-woven fabric), spinning offibers having a fiber diameter of less than 5 μm by the spun bondingmethod reduces a production efficiency and is not practical. The fiberdiameter is more preferably 9 to 150 μm.

[0096] In the filter cartridge of the present invention, a non-wovenfabric prepared by laminating a long fiber non-woven fabric and a meltblown non-woven fabric may be used for the non-woven fabric strip. Inthis case, it can make good use of both advantages of the long fibernon-woven fabric and the melt blown non-woven fabric. Aparticle-trapping performance of the filter cartridge is influenced agreat deal by a fiber diameter of the melt blown non-woven fabric, andthis is particularly preferred when preparing the filter cartridge witha high accuracy.

[0097] The laminating method shall not specifically be restricted. Afiber aggregate of the melt blown non-woven fabric and that of the longfiber non-woven fabric (long fiber web) may be produced respectively atdifferent steps and then superposed, or alternatively, fibers may bemelt-blown directly on the long fiber non-woven fabric or the long fiberweb and laminated. Examples of combinations of the fibers for thelaminated non-woven fabric include two layers of melt blown fiber/longfiber, three layers of long fiber/melt blown fiber/long fiber, and threelayers of melt blown fiber/melt blown fiber/long fiber which comprisetwo melt blown fibers having different fiber diameters.

[0098] In the present invention, yarns having different cross sectionscan be used. They can provide a filter cartridge having the sameliquid-passing property and a higher accuracy, as compared with thefibers having a circular cross section, because an amount of trappedfine particles increases as a surface area of the filter becomes larger.

[0099] In the present invention, the thermoplastic resin used forproducing the thermoplastic fiber can be blended with a hydrophilicresin such as polyvinyl alcohol, or a surface of the non-woven fabricstrip can be subjected to plasma treating, in order to improve theliquid-passing property when using the filter cartridge for filtering awater-based liquid.

[0100] In the present invention, a heat bonding method is preferred as amethod for bonding fiber intersections for preparing the non-wovenfabric from the thermoplastic fiber. The method includes a thermalcompression bonding method by means of an apparatus such as a thermalembossing roll and a heat flat calender roll; and a method using a heattreating machine of a hot blast-circulating type, a heat through-airtype, an infrared heater type or a vertical hot blast-blowing type.Among them, a method using a thermal embossing roll is preferred,because it can elevate a production rate of a non-woven fabric, providesa good productivity and can reduce a cost.

[0101] As shown in FIG. 7, a non-woven fabric produced by the methodusing a thermal embossing roll has part 8 where strong thermalcompression bonding by an embossing pattern is applied and part 9 whereonly weak thermal compression bonding by deviating from an embossingpattern is applied. This makes it possible to trap a lot of foreignmatters 2 in the part 8, and a part of the foreign matters in the part9, while the remaining foreign matters can pass through the long fibernon-woven fabric to move to the following layer. Preferred is this deeplayer-filtering structure, in which even the inside of the filter isutilized. In this case, an embossing patterned area is preferably from 5to 25%. Setting the lower limit of this area to 5% can enhance thefiltering effect exerted by the part 8 and 9, and setting the upperlimit to 25% can control the rigidity of the non-woven fabric not tobecome too high. Further, a part of foreign matters are allowed to passthrough the non-woven fabric strip.

[0102] A composite fiber comprising a low melting resin and a highmelting resin, wherein the melting point difference is 10° C. or more,preferably 15° C. or more, is preferred as the fiber constituting thenon-woven fabric strip. The melting point difference of 10° C. or morestabilizes a heat adhesion property in the fiber intersections of thenon-woven fabric. In the case of a resin having no melting point, theflow-starting temperature is defined as a melting point. Stabilized heatadhesion in the fiber intersections of non-woven fabric strips willallow less particles which have been trapped in the vicinity of thefiber intersections to flow out of filter cartridges, when a filteringpressure and a flow amount of a solution are elevated, and will resultin a less deformation of the filter cartridge. Further, even if asubstance contained in a filtrate deteriorate the fibers, the stabilizedheat adhesion can reduce probability of the fibers falling, and thus itis desirable.

[0103] The composite fiber described above may be in any forms such as aparallel type and a sheath-core type, wherein a low-melting resin ispresent on at least a part of a fiber surface.

[0104] A combination of the low melting resin and the high melting resinin the composite fibers shall not specifically be restricted as long asthe melting point difference is 10° C. or more, preferably 15° C. ormore, which includes linear low density polyethylene/polypropylene, highdensity polyethylene/polypropylene, low densitypolyethylene/polypropylene, copolymer of propylene with othera-olefin/polypropylene, linear low density polyethylene/high densitypolyethylene, low density polyethylene/high density polyethylene,various polyethylenes/thermoplastic polyester, polypropylene/thermoplastic polyester, copolymerized low melting thermoplasticpolyester/thermoplastic polyester, various polyethylenes/nylon 6,polypropylene/nylon 6, nylon 6/nylon 66 and nylon 6/thermoplasticpolyester. Among them, a combination of linear low densitypolyethylene/polypropylene is preferably used, since rigidity and a voidrate of the non-woven fabric strip can readily be controlled during astep of adhesion of fiber intersections in producing the non-wovenfabric. When a filter cartridge is used for filtering a solution of arelatively high temperature, a combination of low meltingpolyester/polyethylene terephthalate can suitably be used, the polyesterbeing prepared by copolymerizing with isophthalic acid.

[0105] In the present invention, other fibers than the thermoplasticfibers may be contained in the non-woven fabric strip as long as theeffect of the present invention is not damaged. Examples of the fibersother than the thermoplastic fibers include rayon, cupra, cotton, hemp,pulp and carbon fiber. The content of the thermoplastic fiber maypreferably be at least 30% by weight, and it can be 100% by weight. Ifit is less than 30% by weight, a strength of the non-woven fabric isreduced when thermally bonded by a thermal compression bonding methodand a through-air heat treating method, so that the fibers are liable tofall off and to be mixed in the filtrate while filtering.

[0106] For preparing the non-woven fabric strip used for the filtercartridge of the present invention, a non-woven fabric-producing set-up,for example, a spinning width may be controlled to directly prepare thenon-woven fabric strip, but preferably, a wide non-woven fabric is slitinto strips.

[0107] A width of the non-woven fabric strip used for the filtercartridge of the present invention is preferably 0.5 to 40 cm. If thiswidth is less than 0.5 cm, the wide non-woven fabric is likely to bebroken when the non-woven fabric is slit into strips, and it isdifficult to control a tension in winding around a perforated cylinderin a twill form. Further, when preparing a filter cartridge having thesame void rate, the winding time is extended and the productivity isreduced. On the other hand, if the width exceeds 40 cm, a friction in ayarn passage of a winder including a traverse guide may be larger or theconverged non-woven fabrics may be irregular in size.

[0108] A basis weight of the non-woven fabric strip, i.e., a weight perunit area of the non-woven fabric is preferably 5 to 200 g/m². If thevalue is smaller than 5 g/m², an amount of the fiber is reduced,resulting in an increased unevenness in the non-woven fabric or areduced strength of the non-woven fabric, or occasionally difficulty inthermal bonding of the fiber intersections. On the other hand, the valuelarger than 200 g/m² will render the rigidity of the non-woven fabrictoo much increased, so that the fabric is difficult to wind around aperforated cylinder in a twill form at the later stage.

[0109] An upper limit of a width of the non-woven fabric strip variesdepending on the basis weight, and a product of a width (cm) and a basisweight (g/m²) of the non-woven fabric strip is preferably 10 to 200 cmg/m². The value larger than 200 will render the rigidity of thenon-woven fabric excessively increased, so that winding of the non-wovenfabric on a perforated cylinder in a twill form becomes difficult at thelater stage. Further, the non-woven fabric becomes too thick inconverging, so that it becomes difficult to wind it densely. On theother hand, if the product is less than 10, the non-woven fabric may becut.

[0110] In the present invention, an airflow amount (cm³/cm²/sec) of thenon-woven fabric strip measured by JIS L 1096-A (1990) method variesdepending on uses of the filter cartridge, and it is preferably 1 to6000 cm³/cm²/sec.

[0111] In the present invention, a thickness of the non-woven fabricstrip is 0.02 to 1.20 mm, preferably 0.05 to 0.90 mm. If a thickness ofthe non-woven fabric strip is less than 0.02 mm, a strength of thenon-woven fabric is reduced, and the non-woven fabric may be cut whenwound around a perforated cylinder in producing a filter cartridge. Onthe other hand, if a thickness of the non-woven fabric strip exceeds1.20 mm, the rigidity may become too high, so that the non-woven fabricis difficult to be wound around a perforated cylinder densely in a twillform.

[0112] The non-woven fabric strip is wound and processed into a form ofa filter cartridge by the method mentioned above. This may be used for afilter cartridge as it is, or a gasket of foamed polyethylene having athickness of approx. 3 mm may be stuck on an end surface of the filtercartridge to improve an adhesion property to housing.

[0113] In the filter cartridge of the present invention, divided fiberscan also be used for the fibers of the non-woven fabric strip. However,since it is actually difficult to evenly divide fibers into dividedfibers, a melt blown non-woven fabric having a similar average fiberdiameter is more preferably used as described above.

[0114] When the non-woven fabric strip is made hydrophilic byincorporating a hydrophilic resin such as polyvinyl alcohol into a rawmaterial resin for the fabric or subjecting the surface thereof toplasma treatment, the liquid-passing property of the resulting filtercartridge can be enhanced in case of filtering an aqueous solution.Accordingly, a filter cartridge using such resin is preferred forfiltering an aqueous solution.

[0115] In the present invention, the filter cartridge thus prepared hasa void rate preferably in a range of 65 to 85%. The value smaller than65% will render the fiber density too high, so that the liquid-passingproperty is reduced. On the contrary, the value larger than 85% willrender the strength of the filter cartridge reduced and often causedeformation of the filter cartridge unfavorably when a high filteringpressure is applied.

[0116] The liquid-passing property can be improved by providing thenon-woven fabric strip with notch or by perforating it. In this case,the number of the notch is preferably 5 to 100 per 10 cm of thenon-woven fabric, and the perforation area is preferably 10 to 80%. Thefiltering performance can be controlled by winding plural non-wovenfabric strips, or winding it together with other yarns such as a spunyarn. A wide non-woven fabric may be wound in a layer form while windingthe non-woven fabric strip in a traversing manner, whereby the maximumflow-out diameter of particles can be controlled when a filter cartridgehaving a rough accuracy is prepared.

[0117] The filter life can be improved by winding a non-woven fabrichaving a high fineness in an internal layer of the filter cartridge andthen winding a non-woven fabric having a low fineness in an externallayer thereof. In this case, a fineness of the external layer is setsuitably 2 to 8 times as low as that of the internal layer. Further, thefilter life can be improved as well by winding a non-woven fabric havinga wide slit width for the internal layer and winding a non-woven fabrichaving a narrow slit width for the external layer. In this case, anon-woven fabric strip width of the internal layer is set suitably 1.5to 10 times as large as that of the external layer. Other methods forimproving the filter life include a method of winding a non-woven fabrichaving a large basis weight for the internal layer and then winding anon-woven fabric having a small basis weight for the external layer, anda method of winding a weakly twisted non-woven fabric for the internallayer and then winding a strongly twisted non-woven fabric for theexternal layer. It is suitable to set a basis weight of the non-wovenfabric in the internal layer 2 to 10 times as large as that of theexternal layer and to set a twist of the non-woven fabric in theexternal layer 2 to 10 times as much as that of the internal layer. Adense and rough structure of the filter cartridge can be formed by thesemethods, and a filter life of the filter cartridge is improved.

[0118] In the present invention, an end face of the filter cartridge maypreferably be smoothened by heat adhesion, which forms smoothend-sealing parts at both ends of the filter cartridge and elevates thesealing property. The non-woven fabric strip constituting both end partsof the filter cartridge is molten by heat, a solvent, a supersonic wave,etc. and then solidified while forming the smooth end faces. Since thenon-woven fabric strip comprising the thermoplastic fiber is used in thepresent invention, a heating method is preferred.

EXAMPLES

[0119] The present invention shall be explained below in detail withreference to examples and comparative examples, but the presentinvention shall not be restricted to these examples. In the respectiveexamples, the physical properties and the filtering performances of thefilters were evaluated by the methods described below.

[0120] Winder and Winding Number

[0121] A winder had a traverse width (width of traversing) of 250 mm, inwhich a hole of a traverse guide 5 shown in FIG. 6 had a diameter of 5mm. An initial speed of a bobbin was set up to 1500 rpm. A windingnumber (W), that is, a number of winding the non-woven fabric striparound a perforated cylinder from one end to the other end wascontrolled by interlocking a reciprocating motion of the traverse guidewith a rotary motion of the perforated cylinder by means of severalgears having an appropriate number of gear teeth.

[0122] Basis Weight and Thickness of Non-woven Fabric

[0123] The non-woven fabric having the area of 625 cm² (Examples 1 to 15and Comparative Examples 1 to 5) or 500 cm2 (Examples 16 to 25 andComparative Examples 6 to 9) was cut off and weighed. The weight wasconverted to a weight per square meter to define a basis weight.Further, the thickness of the cut non-woven fabric was measuredoptionally at 10 points, (Examples 1 to 15 and Comparative Examples 1 to5) or 12 points (Examples 16 to 25 and Comparative Examples 6 to 9), andthe values of 8 points (Examples 1 to 15 and Comparative Examples 1 to5) or 10 points (Examples 16 to 25 and Comparative Examples 6 to 9)excluding the maximum value and the minimum value were averaged todefine the thickness of the non-woven fabric. The thickness at therespective points was measured on the conditions of a load of 196 Pa anda measuring speed of 2 mm/sec by means of “Digithickness Tester (tradename)” manufactured by Toyo Seiki Seisaku-Sho, Ltd.

[0124] Fiber Diameter of Fiber Constituting Non-woven Fabric

[0125] The non-woven fabric was sampled at 5 spots at random, and theywere photographed through a scanning type electron microscope. 20 fibersper spot were selected at random to measure the diameters of the fibers,and an average value thereof was defined as the fiber diameter (μm) ofthe non-woven fabric.

[0126] Airflow Amount

[0127] Measured according to JIS L 1096-A (1990) method. When theairflow amount exceeded 790 cm³/cm²/sec, a measured area of the testsample was reduced.

[0128] Void Rate of Filter Material for Filter Cartridge

[0129] The major diameter, the minor diameter, the length and the weightof the filter cartridge were measured to determine the void rate usingthe following equation. In order to determine the void rate of thefilter material itself excluding a perforated cylinder, the majordiameter of the perforated cylinder was used for the value of the minordiameter, and a value obtained by deducting the weight of the perforatedcylinder from the weight of the filter cartridge was used for the valueof the weight:

(Apparent volume of filter material)={(Major diameter of filtermaterial)²−(Minor diameter of filter material )²}/4×π×(Length of filtermaterial);

(Real volume of filter material)=(Weight of filter material)/(Density ofraw material of filter material);

(Void rate of filter material)={1−(Real volume of filtermaterial)/(Apparent volume of filter material)}×100 (%).

[0130] Initial Trapped Particle Diameter, Initial Pressure Loss andFilter Life

[0131] One filter cartridge was mounted to a housing of a circulatingtype testing machine for filtering performance, and water was passed tocirculate, controlling a flow rate to 30 dm³/minute by means of a pump.A difference in pressures at the inlet and outlet of the filtercartridge was set as an initial pressure loss. Next, a cake prepared bymixing 8 kinds of testing powder I prescribed in JIS Z 8901 (1995)(abbreviated as JIS 8 kinds; intermediate diameter: 6.6. to 8.6 μm) with7 kinds of the same powder (abbreviated as JIS 7 kinds; intermediatediameter: 27 to 31 μm) in a weight ratio of 1:1 was continuously addedat 0.4 g/minute, (Examples 1 to 15 and Comparative Examples 1 to 5), orthe JIS 7 kinds were continuously added at 0.2 g/minute (Examples 16 to25 and Comparative Examples 6 to 9), and the original solution and thefiltrate were sampled 5 minutes after starting of the addition. Theywere diluted to appropriate concentrations, and then the numbers ofparticles contained in the respective solutions were measured by meansof a light shielding type particle detector to calculate an initialtrapping efficiency. Further, the value thereof was interpolated todetermine a particle diameter showing a trapping efficiency of 80%. Theaddition of the cake was still continued until the pressure loss of thefilter cartridge reached to 0.2 MPa, and the original solution and thefiltrate were again sampled to determine a trapped particle diameter.Time consumed from starting addition of the cake until reaching to 0.2MPa was defined as a filter life. When the pressure difference did notreach to 0.2 MPa even the filter life reached to 1000 minutes, themeasurement was discontinued at that point of time.

[0132] Bubbling and Fiber Falling of Initial Filtrate

[0133] One filter cartridge was mounted to a housing of a circulatingtype testing machine for filtering performance, and ion-exchanged waterwas passed, controlling a flow rate to 10000 cm³/minute by means of apump. 1000 cm³ of an initial filtrate was sampled, and 25 cm³ thereofwas taken into a calorimetric bottle and stirred vigorously to observebubbling 10 seconds after stopping the stirring. When a volume of bubble(volume from a liquid surface up to the top of bubble) was 10 cm³ ormore, it was judged poor and shown by a symbol “C”; when a volume ofbubble was less than 10 cm³, it was judged fair and shown by a symbol“B”; and when less than 5 bubbles having a diameter of 1 mm or more wereobserved, it was judged good and shown by a symbol “A”. Further, 500 cm³of the initial filtrate was passed through a nitrocellulose filterhaving a pore diameter of 0.8 μm to judge fiber falling. When the numberof fibers having a length of 1 mm or more per cm² of the filter paperwere 4 or more, it was judged poor and shown by “C”; the number of 1 to3 was judged fair and was shown by “B”; and the number of 0 was judgedgood and shown by “A”.

[0134] Deformation of Filter Cartridge

[0135] One filter cartridge was mounted to a housing (transparent) of acirculating type testing machine for filtering performance, and waterwas passed to circulate, controlling a flow rate to 30 dm³/minute bymeans of a pump. An appearance of the filter cartridge was photographed.The JIS 7 kinds were added until the pressure loss before and after thehousing reached 0.5 MPa. Then, an appearance of the filter cartridge wasphotographed on the same conditions (object distance, magnification,etc.) when the pressure loss before and after the housing reached 0.5MPa. The major diameter of the filter cartridges shown in the twophotographs was measured by image analysis to determine a shrinkagepercentage. A shrinkage less than 10% was judged good and shown by “A”;a shrinkage 10% or more and less than 20% was judged fair and shown by“B” and a shrinkage 20% or more was judged poor and shown by “C”.

Example 1

[0136] Used as a non-woven fabric was a polypropylene melt blownnon-woven fabric having a basis weight of 50 g/m², a thickness of 0.8 mmand a fiber diameter of 82 μm, in which fiber intersections werethermally bonded by remaining heat of spinning and an airflow amount was1400 cm³/cm²/sec. Used for a perforated cylinder was a polypropyleneinjection-molded article having a minor diameter of 30 mm, a majordiameter of 34 mm and a length of 250 mm, and also having 180 holes of 6mm square. The above melt blown non-woven fabric was slit to a width of2.5 cm to obtain a non-woven fabric strip. The strip was passed througha traverse hole of the winder to be converged and wound around theperforated cylinder with a winding number set to 4.429 until the majordiameter reached to 62 mm to obtain a cylindrical filter cartridge 7 asshown in FIG. 8.

Example 2

[0137] A cylindrical filter cartridge was obtained in the same manner asin Example 1, except that used as a non-woven fabric was a polypropylenemelt blown non-woven fabric having a basis weight of 20 g/m², athickness of 0.2 mm and a fiber diameter of 3 μm, in which fiberintersections were thermally bonded by remaining heat of spinning and anairflow amount was 38 cm³/cm²/sec. This filter cartridge had a higherfiltering accuracy than that of the filter cartridge described inExample 1.

Example 3

[0138] Used as a non-woven fabric were the same polypropylene melt blownnon-woven fabric as in Example 2 and a polypropylene spun bonded longfiber non-woven fabric having a basis weight of 20 g/m², a thickness of0.2 mm, a fiber diameter of 18 μm and an airflow amount of 560cm³/cm²/sec. One melt blown non-woven fabric and one spun bonded longfiber non-woven fabric each described above were superposed and thefiber intersections were thermal compression bonded by means of a heatembossing roll at a heat bonded area rate of 13% to prepare a laminatednon-woven fabric. A cylindrical filter cartridge was obtained in thesame manner as in Example 1, except that this non-woven fabric was usedto prepare a non-woven fabric strip having a width of 5 cm. This filtercartridge had almost the same filtering accuracy and an excellent filterlife as compared with the filter cartridge described in Example 2.

Example 4

[0139] Used as a non-woven fabric was a polypropylene spun bonded longfiber non-woven fabric having a basis weight of 20 g/m², a thickness of0.19 mm and a fiber diameter of 18 μm, in which fiber intersections werethermal compression bonded by means of a heat embossing roll at a heatbonded area rate of 13% and an airflow amount was 490 cm³/cm²/sec. Thesame perforated cylinder as in Example 1 was used. The spun bonded longfiber non-woven fabric was slit to a width of 5 cm to obtain a non-wovenfabric strip. The strip was not converged and wound around theperforated cylinder by means of a winder with a winding number set to4.429 until the major diameter reached to 62 mm to obtain a cylindricalfilter cartridge.

Example 5

[0140] The same non-woven fabric strip and perforated cylinder as inExample 1 were used. The non-woven fabric strip was passed through atraverse hole of a winder and converged. It was wound around theperforated cylinder on the same conditions as in Example 4 to obtain afilter cartridge. This filter cartridge had a lower filtering accuracy,a better liquid-passing property and a longer filter life than those ofthe filter cartridge described in Example 4.

Example 6

[0141] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except for changing the raw material resin of the spunbonded long fiber non-woven fabric to polyethylene terephthalate. Thisfilter cartridge showed almost the same filtering performance as that ofthe filter cartridge described in Example 5.

Example 7

[0142] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except for changing the raw material resin of the spunbonded long fiber non-woven fabric to nylon 66. This filter cartridgeshowed almost the same filtering performance as that of the filtercartridge described in Example 5.

Example 8

[0143] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except that sheath-core type composite fibers comprisinghigh density polyethylene as a low melting component and polypropyleneas a high melting component in a weight ratio of 5:5 were used as thestructural fibers for the spun bonded long fiber non-woven fabric. Thisfilter cartridge had a more excellent accuracy than that of the filtercartridge described in Example 5 and showed such an excellent stabilityin the filtering accuracy that the trapped particle diameter at 0.2 MPascarcely changed from the initial trapped particle diameter.

Example 9

[0144] A cylindrical filter cartridge was obtained in the same manner asin Example 8, except that linear low density polyethylene was used asthe low melting component for the sheath-core type composite fiber. Thisfilter cartridge had almost the same filtering accuracy as that of thefilter cartridge obtained in Example 8 and had a more excellentliquid-passing property than that of the filter cartridge described inExample 8.

Example 10

[0145] A cylindrical filter cartridge was obtained in the same manner asin Example 9, except that the thermal bonding method for the fiberintersections was changed from the thermal compression bonding method bya hot embossing roll to a heat treating method by a hotblast-circulating type heating apparatus. This filter cartridge had alittle lower filtering accuracy than that of the filter cartridgedescribed in Example 9.

Example 11

[0146] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except that the long fiber non-woven fabric was slit to awidth of 1 cm and that the winding number was changed to 3.476. Thisfilter cartridge showed almost the same performance as that of thefilter cartridge described in Example 5. However, time required forwinding was longer than in Example 2.

Example 12

[0147] A cylindrical filter cartridge was obtained in the same manner asin Example 11, except that the long fiber non-woven fabric was slit to awidth of 9 cm and that the winding number was changed to 3.714. Thisfilter cartridge had a lower filtering accuracy than that of the filtercartridge described in Example 11, and this may be because the non-wovenfabric strip-converged matter became extremely thick.

Example 13

[0148] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except that a fiber diameter of the fiber constituting thenon-woven fabric strip was changed to 40 μm. This filter cartridge had alower filtering accuracy than that of the filter cartridge described inExample 5.

Example 14

[0149] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except that a basis weight of the non-woven fabric stripwas changed to 44 g/m². This filter cartridge had a lower filteringaccuracy than that of the filter cartridge described in Example 5.

Example 15

[0150] A cylindrical filter cartridge was obtained in the same manner asin Example 5, except that the non-woven fabric strip was twisted 100times per one meter instead of converging. This filter cartridge showedalmost the same filtering performance as that of the filter cartridgedescribed in Example 12.

Comparative Example 1

[0151] A cylindrical filter cartridge was obtained in the same manner asin Example 2, except that polypropylene spun yarns having a diameter of2 mm prepared by spinning fibers having a fiber diameter of 22 μm wasused in place of the non-woven fabric strip. This filter cartridge hadan initial trapped particle diameter larger than that of the filtercartridge described in Example 5 and almost the same as that of thefilter cartridge described in Example 12. However, it had an inferiorliquid-passing property and a shorter filter life than those of thefilter cartridge described in Example 12. Further, bubbling was observedin the initial filtrate, and falling of the filter material was observedas well.

Comparative Example 2

[0152] A cylindrical filter cartridge was obtained in the same manner asin Example 2, except that a filter paper No. 1 prescribed in JIS P 3801(1995), which was cut to a width of 5 cm, was used in place of thenon-woven fabric strip. This filter cartridge had an initial trappedparticle diameter smaller than that of the filter cartridge described inExample 5, but the trapped particle diameter at an elevated pressure waschanged from the initial one to a large extent. Further, the filter lifewas extremely short, and falling of the filter material was observed inthe initial filtrate.

Comparative Example 3

[0153] Short fibers comprising polypropylene and high densitypolyethylene which were dividable to eight parts and had a fiberdiameter of 25 μm were webbed by means of a carding machine, and thewebbed matter was subjected to fiber division and fiber entanglement byhigh pressure water processing to obtain a divided short fiber non-wovenfabric having a basis weight of 22 g/m². This non-woven fabric wasobserved under an electron microscope to carry out image analysis, whichshowed that 50% by weight of the whole fibers was divided into a fiberdiameter of 9 μm. A cylindrical filter cartridge was obtained in thesame manner as in Example 5, except that this non-woven fabric was cutto a width of 5 cm and used in place of the non-woven fabric strip. Aninitial trapped particle diameter in this filter cartridge was smallerthan that in the filter cartridge described in Example 5, but a trappedparticle diameter at 0.2 MPa was larger. Further, a little bubbling inthe initial filtrate was observed as well as falling of the fibers.

Comparative Example 4

[0154] A cylindrical filter cartridge was obtained in the same manner asin Example 11, except that used as a non-woven fabric was apolypropylene melt blown non-woven fabric having a basis weight of 100g/m², a thickness of 1.5 mm and a fiber diameter of 140 μm, in whichfiber intersections were thermally bonded by remaining heat of spinningand an airflow amount was 1400 cm³/cm²/sec. It was difficult to wind thenon-woven fabric densely around the perforated cylinder so that thefiltering accuracy could not be measured.

Comparative Example 5

[0155] A cylindrical filter cartridge was obtained in the same manner asin Example 11, except that used as a non-woven fabric was apolypropylene melt blown non-woven fabric having a basis weight of 140g/m², a thickness of 0.5 mm and a fiber diameter of 90 μm, in whichfiber intersections were thermally bonded by remaining heat of spinningand an airflow amount was 600 cm³/cm²/sec. It was difficult to wind thenon-woven fabric densely around the perforated cylinder as was the casewith Comparative Example 4 so that the filtering accuracy could not bemeasured.

Comparative Example 6

[0156] Used as a non-woven fabric was a polypropylene spun bonded longfiber non-woven fabric having a basis weight of 90 g/m², a thickness of0.80 mm and a fiber diameter of 80 μm, in which fiber intersections werethermally bonded by a heat embossing roll at a heat bonded area rate of13% and an airflow amount was 1000 cm³/cm²/sec. This spun bonded longfiber non-woven fabric was slit into a non-woven fabric strip having awidth of 5 cm. The same perforated cylinder as in Example 1 was used.The strip was passed through a traverse hole of the winder to beconverged and wound around the perforated cylinder with a winding numberset to 4.429 until the major diameter reached to 62 mm to obtain acylindrical filter cartridge as shown in FIG. 8. In this case, neitherequation (A) nor equation (B) was satisfied. As compared with the filtercartridge of Example 4 which had such a high filtering accuracy that aninitial trapped particle diameter was 7 μm, this filter cartridge had aninitial trapped particle diameter of 103 μm, which proved that it couldnot trap fine particles.

Comparative Example 7

[0157] Used as a non-woven fabric was a polypropylene spun bonded longfiber non-woven fabric having a basis weight of 50 g/m², a thickness of0.86 mm and a fiber diameter of 500 μm, in which fiber intersectionswere thermally bonded by a heat embossing roll at a heat bonded arearate of 13% and an airflow amount was 3000 cm³/cm²/sec. This spun bondedlong fiber non-woven fabric was slit into a non-woven fabric striphaving a width of 5 cm. The same perforated cylinder as in Example 1 wasused. The strip was passed through a traverse hole of the winder to beconverged and wound around the perforated cylinder with a winding numberset to 4.429 until the major diameter reached to 62 mm to obtain acylindrical filter cartridge as shown in FIG. 8. In this case, neitherequation (A) nor equation (B) was satisfied. As compared with the filtercartridge of Example 4 which had such a high filtering accuracy that aninitial trapped particle diameter was 7 μm, this filter cartridge had aninitial trapped particle diameter of 349 μm, which proved that it couldnot trap fine particles. TABLE 1 Example 1 2 3 4 5 Non-woven fabricstrip Raw material of fiber*¹ PP PP PP PP PP Fiber diameter μm 82 3 18 &3 18 18 Production process Melt blow Melt blow S + M*² Spun bonding Spunbonding Method for bonding fiber Remaining Remaining Embossing EmbossingEmbossing intersections heat heat Basis weight g/m² 50 20 40 20 20 Widthcm 2.5 5 5 5 5 Thickness mm 0.8 0.2 0.35 0.19 0.19 Airflow amount 140038 35 490 490 cm³/cm²/sec Fitness of equation (A) A A A A A Filtercartridge Processing of non-woven Converging Converging Converging NoneConverging fabric Void rate of filter % 78 80 81 77 81 material Initialtrapped μm 80 8 8 7 13 particle diameter Initial pressure loss MPa 0.0010.025 0.025 0.013 0.003 Trapped particle μm 80 9 9 8 14 diameter in 0.2MPa Filter life min. >1000 20 30 70 215 Bubbling A A A A A Fiber fallingA A A A A 6 7 8 9 10 Non-woven fabric strip Raw material of fiber*¹ PETNylon 66 HDPE/PP LLDPE/PP LLDPE/PP Fiber diameter μm 15 16 18 18 18Production process Spun Spun Spun Spun bonding Spun bonding bondingbonding bonding Method for bonding fiber Embossing Embossing EmbossingEmbossing Hot-air intersections circulating Basis weight g/m² 20 20 2020 20 Width cm 5 5 5 5 5 Thickness mm 0.27 0.23 0.19 0.19 0.19 Airflowamount 600 580 470 470 450 cm³/cm²/sec Fitness of equation (A) A A A A AFilter cartridge Processing of non-woven Converging ConvergingConverging Converging Converging fabric Void rate of filter % 81 81 8080 81 material Initial trapped μm 13 13 12 12 13 particle diameterInitial pressure loss MPa 0.002 0.002 0.003 0.002 0.001 Trapped particleμm 14 14 12 12 13 diameter in 0.2 MPa Filter life min. 210 210 220 220240 Bubbling A A A A A Fiber falling A A A A A

[0158] TABLE 2 Example 11 12 13 14 15 Non-woven fabric strip Rawmaterial of fiber*¹ PP PP PP PP PP Fiber diameter μm 18 18 40 18 18Production process Spun bonding Spun bonding Spun bonding Spun bondingSpun bonding Method for bonding fiber Embossing Embossing EmbossingEmbossing Embossing intersections Basis weight g/m² 20 20 20 44 20 Widthcm 1 9 5 2.5 5 Thickness mm 0.19 0.19 0.19 0.39 0.19 Airflow amountcm³/cm²/sec 490 490 780 260 490 Fitness of equation (A) A A A A A Filtercartridge Processing of non-woven Converging Converging ConvergingConverging Converging fabric Void rate of filter % 80 82 82 80 80material Initial trapped μm 12 18 30 17 13 particle diameter Initialpressure loss MPa 0.003 0.003 0.001 0.003 0.003 Trapped particle μm 1319 30 18 14 diameter in 0.2 MPa Filter life min. 210 630 >1000 620 210Bubbling A A A A A Fiber falling A A A A A Comparative Example 1 2 3 4 5Non-woven fabric strip (Spun yarn) (Filter paper) Raw material offiber*¹ PP Cellulose HDPE/PP PP PP Fiber diameter μm — — 9 140 90Production process — — (Fiber Melt blow Melt blow confounding) Methodfor bonding fiber — — (High pressure Remaining Remaining intersectionswater) heat heat Basis weight g/m² — 90 22 100 140 Width cm — 1.5 5 1 1Thickness mm — 0.2 0.2 1.5 0.5 Airflow amount cm³/cm²/sec 150 1400 600Fitness of equation (A) — — A C C Filter cartridge Processing ofnon-woven — None None Converging Converging fabric Void rate of filter %76 72 77 — — material Initial trapped μm 18 11 10 — — particle diameterInitial pressure loss MPa 0.005 0.022 0.010 — — Trapped particle μm 2220 13 — diameter in 0.2 MPa Filter life min. 280 30 80 — — Bubbling C AB — — Fiber falling C C C — —

Example 16

[0159] Used as a non-woven fabric was a polypropylene long fibernon-woven fabric obtained by a spun bonding method. The fiberintersections were thermally bonded by a thermal compression bondingmethod by means of a heat embossing roll. The non-woven fabric had abasis weight of 22 g/m², a thickness of 200 μm and an average fiberdiameter of 17 μm. The long fiber non-woven fabric was slit to a widthof 50 mm to prepare a non-woven fabric strip. Further, used for aperforated cylinder was a polypropylene injection-molded article havinga minor diameter 30 mm, a major diameter of 34 mm and a length of 250mm, and also having 180 holes of 6 mm square. A winding number (W) of awinder was set up to 3.1875 (M₂ in the equation (3) is 8 in this case).The non-woven fabric strip was passed through a hole of a traverse guidein the winder and converged, and it was wound around the perforatedcylinder until a major diameter reached to 60 mm to obtain a cylindricalfilter cartridge. Both end faces thereof were welded by heating for 5seconds by means of a hot plate having a surface temperature of 175° C.to obtain a cylindrical filter cartridge as shown in FIG. 8. Neitherbubbling nor falling of the filter material was observed and thepressure loss was small, and thus, the filter cartridge was provedexcellent.

Examples 17 to 21

[0160] Cylindrical filter cartridges were obtained in the same mannerusing the same non-woven fabric strip and perforated cylinder as inExample 16, except that the winding numbers (W) were set to 3.2778(Example 17), 3.2917 5 (Example 18), 3.3847 (Example 19), 3.4118(Example 20) and 3.1885 (Example 21), respectively. When the 2-foldvalues (2W) of these winding numbers (W) are approximated to fractionshaving denominators (M₂) of two figures or less, the denominators are 9,12, 13, 17 and 61, respectively. As these filter cartridges had largerM₂, the initial trapped particle diameters became smaller. Accordingly,the value of M₂ correlates with the initial trapped particle diameter.When 2W are approximated to fractions having denominators (M₃) of threefigures or less, the initial trapped particle diameter does not decreasein proportion to the denominator (M₃). For example, M₃ is larger inExample 20 than in Example 21, but the initial trapped particle diameteris smaller in Example 21. Thus, it proves that M₃ in the equation (3)does not correlate with the filtering accuracy. The winding number W issmaller in Example 20 than in Example 21, but the initial trappedparticle diameter is smaller in Example 21. Thus, it proves that theinitial trapped particle diameter does not increase in proportion to thewinding number W. The filter described in Example 21 had a relativelylarge pressure loss and a little poor liquid-passing property ascompared with the other filters.

Examples 22 and 23

[0161] Cylindrical filter cartridges were obtained in the same manner asin Example 19, except that a width of the non-woven fabric strip waschanged to 2 cm (Example 22) or 3 cm (Example 23). These filtercartridges had large initial trapped particle diameters as compared withthat of the filter cartridge described in Example 19.

Example 24

[0162] A cylindrical filter cartridge was obtained in the same manner asin Example 19, except that used as a non-woven fabric strip was a meltblown non-woven fabric having an average fiber diameter of 2 μm, a basisweight of 22 g/m² and a width of 5 cm. This filter cartridge had a smallinitial trapped particle diameter as compared with that of the filtercartridge described in Example 19.

Example 25

[0163] A cylindrical filter cartridge was obtained on the sameconditions as in Example 19, except that used as a non-woven fabricstrip was a laminated non-woven fabric obtained by thermal compressionbonding by means of a heat embossing roll, which comprised three kindsof non-woven fabrics: a polypropylene long fiber non-woven fabric havinga basis weight of 5 g/m² and a fineness of 2 dtex which was obtained bya spun bonding method, a melt blown non-woven fabric having an averagefiber diameter of 2 μm, a basis weight of 22 g/m² and a width of 5 cm,and a polypropylene long fiber non-woven fabric having a basis weight of5 g/m² and a fineness of 2 dtex which was obtained by the spun bondingmethod. This filter cartridge had a small initial trapped particlediameter as compared with that of the filter cartridge described inExample 19.

Comparative Example 8

[0164] A polypropylene short fiber having a fineness of 2 dtex, a cutlength of 51 mm and a crimp number of 14 was formed by conventional meltspinning, and it was spun to obtain a spun yarn. The spun yarn was woundaround the same perforated cylinder as in Example 16 with a windingnumber (W) set to 3.2252 to obtain a filter cartridge. Both end facesthereof were welded by heating for 5 seconds by means of a hot platehaving a surface temperature of 175° C. to obtain a filter cartridge.This filter cartridge was uneven on the end face and inferior in asealing property of the end face. The initial trapped particle diameterthereof was in-between of the initial trapped particle diameters inExamples 19 and 20, but it had a larger pressure loss than those of bothExamples 19 and 20 and an inferior liquid-passing property. Further,bubbling and the fibers fallen off the filter material were observed inthe filtrate, and therefore, it was not preferred as a filter cartridge.Comparative Example 9.

[0165] A filter cartridge was obtained in the same manner using the samematerials as in Example 16, except that the winding number (W) waschanged to 0.6538. The wound non-woven fabric strip was liable to comeoff this filter cartridge, and it was not suited for a filter cartridge.

Comparative Example 10

[0166] A filter cartridge was obtained in the same manner using the samematerials as in Example 16, except that the winding number (W) waschanged to 10.1923. The wound non-woven fabric strip was liable to comeoff this filter cartridge, and it was not suited for a filter cartridge.

Comparative Example 11

[0167] Used as a structural fiber for the non-woven fabric strip wereshort fibers comprising polypropylene and high density polyethylenewhich were dividable into eight parts in a fiber cross section and had afineness of 2 dtex and a fiber length of 64 mm. This dividable shortfiber was webbed by processing by means of a carding machine, and thewebbed matter was processed by means of a heat embossing roll to preparea non-woven fabric. The non-woven fabric was treated twice by means of awater jet apparatus to divide the fiber into a divided non-woven fabrichaving a basis weight of 22 g/m² and a thickness of 210 μm. Thenon-woven fabric was slit to a width of 50 mm to prepare a non-wovenfabric strip. Further, a winding number (W) of a winder was set up to3.1875 (M₂ in the equation (3) is 8 in this case). The non-woven fabricstrip was passed through a hole of a traverse guide in the winder andconverged, and it was wound around a perforated cylinder until a majordiameter reached to 60 mm to obtain a cylindrical filter cartridge. Bothend faces thereof were welded by heating for 5 seconds by means of a hotplate having a surface temperature of 175° C. to obtain a filtercartridge. The filter cartridge thus obtained had a little reducedfiltering accuracy as compared with Example 16. A little bubbling andfalling of the filter material were observed in the filtrate, and thepressure loss was large. Further, the filter cartridge was liable to bedeformed, and it was judged that its use needs a lot of attention incase of the large pressure.

Comparative Example 12

[0168] Used as a non-woven fabric was the same polypropylene spun bondedlong fiber non-woven fabric as in Example 16. This fabric was slit intoa non-woven fabric strip having a width of 5 cm. The same perforatedcylinder as in Example 16 was used. The strip was passed through a holeof a traverse guide in the winder to be converged and wound around aperforated cylinder with a winder number set to 0.8077 until a majordiameter reached to 62 mm to obtain a cylindrical filter cartridge asshown in FIG. 8. As compared with the filter cartridge of Example 16having an initial trapped particle diameter of 59 μm, this filtercartridge had an initial trapped particle diameter of 300 μm, whichproved that it could not trap fine particles.

Comparative Example 13

[0169] Used as a non-woven fabric was the same polypropylene spun bondedlong fiber non-woven fabric as in Example 16. This fabric was slit intoa non-woven fabric strip having a width of 5 cm. The same perforatedcylinder as in Example 16 was used. The strip was passed through a holeof a traverse guide in the winder to be converged and wound around aperforated cylinder with a winder number set to 10.0381 until a majordiameter reached to 62 mm to obtain a cylindrical filter cartridge asshown in FIG. 8. As compared with the cartridge filter of Example 16having a initial trapped particle diameter of 59 μm, this cartridgefilter has a initial trapped particle diameter of 500 μm, which provedthat it could not trap fine particles. TABLE 3 Approximation of 2WApproximation of 2W Basis with denominator of with denominator ofNon-woven Width weight W two figures M₂ three figures M₃ fabric cm g/cm²Example 16 3.1875 6 and 3/8  8 6 and 3/8   8 S 5 22 Example 17 3.2778 6and 5/9  9 6 and 5/9   9 S 5 22 Example 18 3.2917 6 and 7/12  12 6 and7/12   12 S 5 15 Example 19 3.3847 6 and 10/13 13 6 and 347/451 451 S 522 Example 20 3.4118 6 and 14/17 17 6 and 691/839 839 S 5 22 Example 213.1885 6 and 23/61 61 6 and 118/313 313 S 5 22 Example 22 3.3847 6 and10/13 13 6 and 347/451 451 S 2 22 Example 23 3.3847 6 and 10/13 13 6 and347/451 451 S 3 22 Example 24 3.3847 6 and 10/13 13 6 and 347/451 451 M5 22 Example 25 3.3847 6 and 10/13 13 6 and 347/451 451 SMS 5 32Comparative 3.2252 6 and 9/20  13 6 and 168/373 373 Spun yarn 0.3 —Example 8 Comparative 0.6538 1 and 4/13  13 1 and 255/829 829 S 5 22Example 9 Comparative 10.1923 20 and 5/13  13 20 and 5/13   13 S 5 22Example 10 Comparative 3.1875 6 and 3/8 8 6 and 3/8   8 Divided 5 22Example 11 yarns 80% trapped Width × Void particle Pressure Fallingbasis weight rate diameter loss of filter cm × g/cm² % μm MPa Bubblingmaterial Deformation Example 16 110 85 59 0.003 A A A Example 17 110 8239 0.004 A A A Example 18 75 76 8.3 0.018 A A A Example 19 110 81 270.006 A A A Example 20 110 76 7.5 0.020 A A A Example 21 110 74 5 0.030A A A Example 22 44 81 28 0.005 A A A Example 23 66 78 17 0.009 A A AExample 24 110 81 20 0.006 A A A Example 25 160 81 20 0.006 A A AComparative — 70 10 0.030 C C B Example 8 Comparative 110 — — — — — —Example 9 Comparative 110 — — — — — — Example 10 Comparative 110 85 500.004 B B C Example 11

[0170] Effects of the Invention

[0171] The filter cartridge of the present invention has a highfiltering accuracy, a long filter life and a good liquid-passingproperty, in which an initial trapped particle diameter little changes,a pressure loss is small and neither bubbling nor falling of the filtermaterial is observed, as compared with a conventional bobbin winder typefilter cartridge.

What is claimed is:
 1. A filter cartridge which is prepared by winding a non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein the non-woven fabric strip satisfies the following equation (A): log ₁₀ Y<3.75−0.6(log ₁₀ X)  (A) wherein X (cm³/cm²/sec) is an airflow amount of the non-woven fabric strip measured in accordance with JIS L 1096-A (1990), and Y (g/m²) is a basis weight thereof.
 2. A filter cartridge which is prepared by winding a long fiber non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein the non-woven fabric strip satisfies the following equation (B): log ₁₀ Y<3.75−0.75(log ₁₀ X)  (B) wherein X (cm³/cm²/sec) is an airflow amount of the non-woven fabric strip measured in accordance with JIS L 1096-A (1990), and Y (g/m²) is a basis weight thereof.
 3. A filter cartridge which is prepared by winding a non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein in winding in a twill form, a number (W) of winding the non-woven fabric strip from one end to the other end in a longitudinal direction of the perforated cylinder is one to 10 per a length of 250 mm in the perforated cylinder.
 4. The filter cartridge as claimed in claim 3, wherein when a 2-fold value (2W) of the winding number (W) is represented by a fraction having a denominator of two figures or less which is a non-reducible approximate value, the denominator is 4 to
 40. 5. The filter cartridge as claimed in any one of claims 1 to 3, wherein at least a part of fiber intersections of the non-woven fabric strip is thermally bonded.
 6. The filter cartridge as claimed in any one of claims 1 to 3, wherein the non-woven fabric strip has a width of 0.5 to 40 cm.
 7. The filter cartridge as claimed in any one of claims 1 to 3, wherein a product of a width (cm) and a basis weight (g/m²) of the non-woven fabric strip is 10 to
 200. 8. The filter cartridge as claimed in any one of claims 1 to 3, wherein the non-woven fabric strip has a thickness of 0.02 to 1.20 mm.
 9. The filter cartridge as claimed in any one of claims 1 to 3, wherein the non-woven fabric strip is thermal compression bonded by means of a heat embossing roll having an embossing area rate of 5 to 25%.
 10. The filter cartridge as claimed in any one of claims 1 to 3, wherein the filter material of the filter cartridge has a void rate of 65 to 85%.
 11. The filter cartridge as claimed in claim 1 or 3, wherein the non-woven fabric strip is of a long fiber non-woven fabric.
 12. The filter cartridge as claimed in claim 11, wherein the long fiber non-woven fabric is produced by a spun bonding method.
 13. The filter cartridge as claimed in claim 1 or 3, wherein the non-woven fabric strip is of a melt blown non-woven fabric.
 14. The filter cartridge as claimed in any one of claims 1 to 3, wherein the thermoplastic fiber is a composite fiber comprising a low melting resin and a high melting resin, a difference of the melting points between these resins being 10° C. or more.
 15. The filter cartridge as claimed in any one of claims 1 to 3, wherein the thermoplastic fiber is a fiber formed from at least one thermoplastic resin selected from the group consisting of a polyester resin, a polyamide resin, a polyethylene resin and a polypropylene resin.
 16. A process for producing a filter cartridge, which comprises winding a non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein the non-woven fabric strip satisfies the following equation (A): log ₁₀ Y<3.75−0.6(log ₁₀ X)  (A) wherein X (cm³/cm²/sec) is an airflow amount of the non-woven fabric strip measured in accordance with JIS L 1096-A (1990), and Y (g/m²), and Y (g/m²) is a basis weight thereof.
 17. A process for producing a filter cartridge, which comprises winding a non-woven fabric strip comprising a thermoplastic fiber around a perforated cylinder in a twill form, wherein in winding in a twill form, a number (W) of winding the non-woven fabric strip from one end to the other end in a longitudinal direction of the perforated cylinder is one to 10 per a length of 250 mm in the perforated cylinder. 